As I said in the post, if your paid account expires, you won't be able to access any extra icon slots that you bought: just like if you had a paid account (100 icons) and your account expired to a free account (15 icons) you would have 85 icons marked as 'inactive' (until you renewed your account, and then they'd be reactivated!), if you had a paid account (100 icons) with another 20 extra icon slots bought (for 120 total) and your account expired to a free account (15 icons), you would have 105 icons marked as 'inactive' (until you renewed your account, and then they'd be reactivated).

(This is the same way LiveJournal handles its extra icon add-ons, except ours are permanent rather than needing to be renewed. We laid out our reasoning, explained the way it would work, and solicited feedback in a dw-biz post several months ago.)

Believe me, I'd love it if we could offer everybody tons of icons for free permanently! But if we did that, we would very shortly go out of business, and then we would not be able to offer anybody any icons at all :)